With the improvement in functions of a resin itself and in molding technique as background, resin molded products have been recently used in various fields for responding to the demand for the reduction in weight and cost. The field of automobile industries is not exceptional so that the resin molded products have been used for engine components, airbag apparatus components, interior and exterior components (an instrument panel, a duct, a door trim, a glove box, a center console, and a bumper). With increasing number of components of the resin molded product, cases where two resin-molded products are joined together have also been increased. In the case of a thermoplastic resin-molded product, a deposition technique by heating a resin molded product is generally adopted. Its heat source may include a heater, frictional heat, induction heat, laser heat, and radiation heat; whereas, in the field of automobile industries, the vibration welding using the frictional heat has been widely used (see Japanese Unexamined Patent Application Publication No. 2004-276797, for example).
The vibration welding is a method for welding workpieces together by placing one workpiece on another so that vibration is applied to the pressurized workpieces in a predetermined direction so as to generate frictional heat. The invention described in Japanese Unexamined Patent Application Publication No. 2004-276797 relates to a device for mounting an airbag apparatus in that when an instrument panel (welding workpiece) and an airbag-mounting gadget (workpiece to be welded) are welded together, even if the junction position is deviated, the deviation can be easily recognized to be allowable for normally developing of the airbag.
However, the object of the invention described in Japanese Unexamined Patent Application Publication No. 2004-276797, on the assumption that the junction position between workpieces is deviated, is to determine whether the deviation is within the allowable range, so that the invention is not for reducing the deviation itself of the junction position.
The reasons for the deviation injunction position during the vibration welding include an excitation force during vibration and the positional displacement already made at the step of placing one workpiece on the other. In order to reduce the deviation, generally, a positioning rib may be raised from a workpiece to be welded; a positioning jig may be used; or while a positioning pin is raised from a workpiece to be welded, a hole may be formed through the junction of the workpieces for inserting the pin. When the die releasing direction is the same during the molding of the workpieces, the positioning rib or jig can be precisely abutted to the outer peripheral junction face of the workpieces, or the positioning pin can also be inserted into the workpiece hole precisely.
However, the die releasing direction is not always the same during the molding of the workpieces. FIG. 9 herein includes arrangement drawings of an outer panel and an inner case of a conventional airbag apparatus, in which FIG. 9(A) shows a case having a positioning rib; FIG. 9(B) shows a case having a positioning pin; and FIG. 9(C) shows a case where the junction position is deviated.
An outer panel 91 shown in FIG. 9 is a panel with a surface (surface opposite to the attaching surface of an inner case 92) forming part of an instrument panel. After the inner case 92 is welded to the outer panel 91 as shown in the drawing, other components of the airbag apparatus are mounted by conversion and the outer panel 91 is fixed on the instrument panel with the surface facing a cabin and the surface attaching the inner case 92 facing a vehicle body. The outer panel 91 shown in FIG. 9(A) is provided with positioning ribs 91a and 91b raised therefrom, and the outer panel 91 shown in FIG. 9(B) is provided with positioning pins 91c and 91c raised therefrom.
The inner case 92 is a component, called an airbag attaching gadget or bracket, for supporting a retainer accommodating an airbag therein or for gate-opening the outer panel 91 during the inflating and developing the airbag. The inner case 92 includes an inner panel 92a, and the inner panel 92a and the outer panel 91 are vibration-welded together. Also, the inner panel 92a shown in FIG. 9(B) is provided with holes 92b formed to be inserted by positioning pins 91c, respectively.
When the outer panel 91 is fixed to an inclined instrument panel, the die releasing direction may be different during the molding the inner case 92 (the welding workpiece) and the outer panel 91 (the workpiece to be welded). For example, as shown in FIG. 9, the die releasing direction P of the outer panel 91 may be roughly vertical while the die releasing direction Q of the inner case 92 may be roughly vertical to the inclined surface of the outer panel 91. The angle between the die releasing directions P and Q is assumed to be α.
At this time, in the conventional example shown in FIG. 9(A), the outer peripheral face of the inner panel 92a is not in parallel with the rib 91b, so that a clearance of an angle α is produced. Also, in the conventional example shown in FIG. 9(B), the plane, on which the hole 92b of the inner panel 92a is formed, is not in parallel with the pin 91c, so that a clearance of an angle α is produced. Recently, the inclination of the instrument panel has had a tendency to increase in design approach, so that the clearance of the angle α is also liable to increase.
When a clearance is produced between the outer peripheral face of the inner panel 92a and the rib 91b in such a manner, problems arise in that the inner panel 92a runs on the rib 91b as shown in FIG. 9(C) when the inner case 92 is placed on the outer panel 91 or during the vibration welding as well as skilled workers are needed for operation, resulting in the deterioration in yield. Such problems are not limited to the example of the airbag apparatus described above, so that they are common to cases where workpieces different in die releasing direction are welded together.